Field of the Invention
This invention relates to a cardioplegia apparatus and method for automated arresting of a beating heart during cardiac surgery.
Description of the Related Art
In the performance of open heart surgery, the patient is supported by an extracorporeal blood circuit employing a heart/lung machine. The heart is isolated from the vascular system, and venous blood is diverted into the extracorporeal blood circuit where it is oxygenated, temperature-controlled and returned to the patient's arterial side. A separate circuit is established for supplying a cardioplegia solution to the heart as the surgery proceeds.
The cardioplegia circuit functions to still the heart, lower the metabolic requirements of the heart, protect the heart during periods of ischemia and, finally, prepare the heart for reperfusion at the end of the procedure. Operation of the extracorporeal blood circuit as well as the cardioplegia delivery is performed by a trained perfusionist under the direction of the surgeon. The principal elements of cardioplegia solution are blood, representing a small fraction diverted from the output of the heart/lung machine, combined with a crystalloid solution. In addition, an amount of potassium solution is added to the cardioplegia flow to still the heart.
Depending upon the requirements of the particular surgery, the cardioplegia solution may be cooled or warmed, and may be delivered in antegrade fashion to the aortic root or coronary ostia, or in a retrograde mode to the coronary sinus. The requirements placed upon the cardioplegia solution vary as the surgery proceeds, and are subject to the clinical judgment of individual surgeons.
By way of background, an early cardioplegia delivery system typically employed two tubes supplying the blood solution and the crystalloid solution respectively that were routed through a single rotary peristaltic pump whereupon the separate blood and crystalloid solutions in the respective tubes were combined into a single flow delivery line. The ratio between the blood solution and the crystalloid solution was determined by the relative diameters of the respective tubing carrying the two solutions, since each was mounted on the same rotary peristaltic mechanism and thus was forwarded by the same action. The tubing was usually provided in a 4:1 ratio of blood-to-crystalloid cross-sectional flow area, so that the rotary peristaltic pump would be delivering the blood solution and the crystalloid solution to the delivery line in a ratio of approximately 4:1. Potassium was typically provided to the delivery line upstream of the pump from two alternate crystalloid solutions containing potassium, one having a relatively low concentration of potassium, the other a higher concentration. The higher potassium concentration was utilized to arrest the heart, while the lower was used to maintain the stilled condition. While monitoring of the patient's condition during surgery, the perfusionist would select the higher concentration to provide sufficient potassium in the cardioplegia solution to establish the stilled condition of the heart and then select the lower concentration to maintain the heart in a stilled condition. The perfusionist would minimize the delivery of excessive potassium thereby minimizing the risks associated with hyperkalemia.
Early cardioplegia delivery systems were characterized by poor adaptability to varying requirements as may be required by the surgeon during surgery, such as the ratios of the solutions in the delivery flow and the control of the temperature of the delivery flow. The systems suffered from particularly poor control over the cardioplegia delivery flow at low flow rates. Moreover, the blood in the cardioplegia line was subjected to the peristaltic pumping action that produced shearing forces on the blood, thereby risking damage to the blood.
Representative early cardioplegia apparatuses and methods are disclosed in the following United States Patents (and Technical Disclosure), the disclosure of each of which is hereby incorporated by reference herein:
Pat. No.TitleT994001Hypothermic cardioplegia administration set4,416,280Cardioplegia delivery system4,568,330Cardioplegia delivery system with improved bubble trap
One embodiment of an improved cardioplegia apparatus and method that has achieved substantial commercial success is known as the Myocardial Protection System sold under registered trademark “MPS” by Quest Medical, Inc., the assignee of the present invention. The functionality of Quest's MPS Myocardial Protection System is disclosed in U.S. Pat. No. 5,385,540, now Reissue U.S. Pat. No. 36,386, entitled Cardioplegia Delivery System, the disclosure of which is hereby incorporated by reference herein.
Quest's MPS Myocardial Protection System included an extracorporeal blood circuit having a first tube that was connected in fluid communication with a heart/lung machine to divert a portion of the blood flow from the heart/lung machine. A first pump combined blood from the first conduit with a crystalloid solution, and delivered the combined flow into a delivery line. The delivery line was connected in heat-exchanging communication with a heat exchanger to control the temperature of the cardioplegia in the delivery line. A second pump was provided for delivering a potassium solution into the delivery line downstream from the first pump at a flow rate less than 10% of the flow rate of the combined output of the first pump.
Quest's MPS Myocardial Protection System further included control means for adjusting the ratio of blood and crystalloid solution delivered by the first pump, for adjusting the total volumetric rate of flow from the first pump, and for controlling the operation of the second pump so that the volumetric rate of flow of the potassium solution was maintained at a selected percentage of the flow rate from the first pump.
In a preferred mode of operation of Quest's MPS Myocardial Protection System, the first pump employed two pumping chambers, so that one chamber could be refilled while the other was emptying, whereby substantially continuous flow from the first pump could be achieved. The second pump preferably comprised a positive displacement pump, either a syringe or a volumetric pouch configuration containing the potassium solution driven at a rate controlled by the control means. The output of the second pump joined the delivery line downstream from the first pump.
Quest's MPS Myocardial Protection System included a heat exchanger to both heat and cool the cardioplegia solution, and operated under the control of the control means. The first pump included at least one disposable in-line bladder and a separate drive means for changing the volume of the bladder. A fill cycle of the first pump comprised two separate time segments, including a first period for introduction of blood from the main extracorporeal blood circuit and a second period for the introduction of a second fluid, whereby the blood and the second fluid were combined in the bladder in a selected ratio before being forwarded from the first pump. The pressure of the cardioplegia solution was sensed, monitored, and controlled by the control means within safe operating limits.
Quest's MPS Myocardial Protection System further provided a disposable cassette including a delivery set for providing the medications to the patient. A representative cassette is more particularly described in U.S. Pat. No. 5,588,816, entitled Disposable Cassette for Cardioplegia Delivery System, the disclosure of which is hereby incorporated by reference herein.
As shown in FIG. 1A, a further improvement to Quest's MPS Myocardial Protection System involved a display control system (DCS), such as that disclosed in U.S. Pat. No. 5,573,502, entitled “Display Panel and Controls for Blood Mixture Delivery System”, the disclosure of which is hereby incorporated by reference herein. All of the major operating conditions of Quest's MPS Myocardial Protection System including the desired volumetric rates, the desired ratios and percentages of blood, second fluid, third fluid, and any additional fluids, the output temperature and heating and cooling of the output fluid as well as the appropriate operating pressures and safety pressure conditions for either antegrade or retrograde cardioplegia, were conveniently controlled from the display panel connected to the cardioplegia system through a microprocessor control section. This advantageously freed perfusionists, surgeons and other healthcare professionals performing delicate medical procedures, from the complex, cumbersome and sometimes confusing manual rigging, connecting, heating, cooling, monitoring and adjusting of all the various aspects of the prior cardioplegia systems. The centralized control resulted in increased safety and quality of cardioplegia fluid delivery. The system was easily adaptable and adjustable to the particular requirements of a given patient.
While Quest's MPS Myocardial Protection System provided the surgeon with flexibility to continually change the mix, temperature, flow rate and precise quantities of medications delivered to the patient during open-heart surgery, the present invention provides substantial improvements to the functionality of Quest's MPS Myocardial Protection System. Further, as shown in FIG. 1B in comparison with FIG. 1A, the present invention provides a graphical user interface (GUI) to the Quest's MPS Myocardial Protection System.
Quest's MPS Myocardial Protection System comprised three sub-systems:                PMS—Pump Monitoring sub-system        PCS—Pump Control sub-system        DCS—Display Control sub-system        
The sub-systems PMS and PCS were dedicated to the pump operation whereas the DCS sub-system was dedicated to the User Interface consisting of LED's, switches, displays & knobs. As used herein, the MPS Console comprises a Pump Monitoring Subsystem (PMS) and a Pump Control Subsystem (PCS).